Abstract
This study proposes an iterative, joint channel estimation, equalization, and data detection method in the presence of high mobility for a multicarrier downlink system that communicates over rapidly time‐varying channels. The proposed method uses a basis expansion method (BEM) which has low computational complexity and helps to reduce the number of coefficients needed to represent a time‐varying channel and therefore is extremely easy to implement practically. Unlike the current literature, which is almost entirely focused on the uplink communication systems due to their computational costs, this method prioritizes the goal of being feasible in a downlink system with a reasonable performance. The proposed suboptimal algorithm is based on the space‐alternating generalized expectation‐maximization (SAGE) algorithm and the time‐varying channel is represented by orthogonal basis functions obtained by means of discrete Walsh‐Hadamard transform (DWHT). The resulting receiver iterates between maximum a posteriori (MAP) based channel estimation in the subspace spanned by the orthogonal basis functions and successive interference cancellation. Numerical examples show that the proposed algorithm has a satisfactory symbol error rate with low computational complexity and also has a reasonable peak‐to‐average power ratio (PAPR) reduction effect.
Highlights
If the symbol duration is smaller than the channel delay, multipath propagation causes serious multiple access interference (MAI) and intersymbol interference (ISI)
We propose an iterative joint channel estimation, equalization, and data detection method for downlink communication of Multicarrier code division multiple access (MC-code division multiple access (CDMA)) systems communicating with frequency selective and time-varying channels
discrete Walsh-Hadamard transform (DWHT) has been chosen in particular because it has a low computational cost and it can be implemented in hardware with simple addition and subtraction operations
Summary
Some of these studies show that jointly estimate of channel coefficients and user’s data is a good alternative for the downlink communication of MC-CDMA system to improve the performance. In [27], a massive multiple-input multiple-output (MIMO) system with equipped antenna array is considered under the assumption of time-selective flat-fading channel It presents a discrete Fourier transform based spatial-temporal basis expansion model to reduce number of channel coefficients. Instead of the channel coefficients, resulting low dimensional representations of them are estimated and data symbols are detected iteratively with a reasonable computational complexity for the mobile user equipment. This is because DWHT needs simple addition and subtraction without the scaling factor. IN represents the N × N identity matrix and 1N is N × 1 vector each element of which is 1
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